1. Field of the Invention
The present invention relates to an oleophilic molybdenum compound for use in hydroconversion of a hydrocarbon, and a method for producing the same. More particularly, the present invention is concerned with a novel oleophilic molybdenum compound comprising an aliphatic amine group and a heteropolyanion group, which compound is a catalyst precursor capable of being changed, in the hydroconversion reaction system, to a catalyst having excellent catalytic activity in hydroconversion of a hydrocarbon feedstock to a hydrocarbon product having a decreased molecular weight. The present invention is further concerned with a method for efficiently producing the novel oleophilic molybdenum compound from an aliphatic amine and a heteropolyacid.
2. Discussion of Related Art
A hydroconversion is now widely being conducted, in which a hydrocarbon feedstock, particularly a feedstock of a heavy hydrocarbon, such as heavy crude oil, distillation residual oil, tar sand extract oil, shale oil and coal, is converted to a light hydrocarbon having a low molecular weight. In the hydroconversion of a hydrocarbon feedstock, first, the hydrocarbon is thermally cracked to form hydrocarbon radicals. These hydrocarbon radicals are favorably bonded with hydrogen atoms to produce a hydrocarbon having a decreased molecular weight. At the same time, polycondensation of these radicals unfavorably occurs to produce polycondensates, such as coke and asphaltene. These polycondensates are likely to remain in a reaction apparatus, especially in a reaction zone of the apparatus, to thereby cause coking and choking phenomena which hinder the advancement of the hydroconversion reaction. Various catalysts have been proposed, which are expected to exert various activities, including not only an activity of suppressing the above-mentioned unfavorable polycondensation of hydrocarbon radicals while suppressing extreme generation of gases, such as methane, ethane, propane and butane, but also an activity of simultaneously attaining a content decrease with respect to heteroatoms, such as atoms of sulfur, nitrogen and oxygen, heavy metals, such as vanadium and nickel, and ash as contained in the hydrocarbon feedstock and an activity of attaining a hydrogenation of a hydrocarbon so as to modify the properties of the hydrocarbon. These activities of the catalyst are hereinafter frequently referred to simply as "hydroconversion activities".
The conventional reaction systems for the hydroconversion of a heavy oil are classified into three types, i.e., a fixed bed reaction system, an ebullated bed reaction system and a dispersion (suspension) reaction system, depending on how the catalyst is used. Of these, a dispersion reaction system, in which a dispersible metal compound is added as a hydroconversion catalyst or as a precursor thereof to a hydrocarbon feedstock, is preferred from the viewpoint of its suitability for effective hydroconversion of a heavy hydrocarbon feedstock. Accordingly, a large variety of dispersible metal compounds have been proposed for use in the dispersion reaction system.
Most of such dispersible metal compounds contain a metal element selected from transition metal elements of Group V, Group VI and Group VIII of the periodic table. In particular, the most representative element contained in such dispersible metal compounds is a molybdenum element capable of exerting a high catalytic activity in the form of a sulfide or a sulfide-like compound when it is incorporated in a hydrocarbon reaction system. Further, various proposals have been made with respect to the molybdenum compounds which are added as a catalyst precursor to a hydrocarbon feedstock The proposed catalyst precursors include a heteropolyacid containing molybdenum atoms as polyatoms.
U.S. Pat. Nos. 4,134,825, 4,431,520 and 4,606,809 discloses proposals, in which a heteropolyacid containing molybdenum atoms as polyatoms is used in the same way as other metal compounds for the hydroconversion of a hydrocarbon. Further, U.S. Pat. Nos. 4,196,072, 4,637,870 and 4,637,871 disclose the use of a heteropolyacid containing molybdenum or tungusten atoms as polyatoms, optionally together with phosphoric acid. In these U.S. patents, the heteropolyacid is added in the form of a solid or an aqueous solution.
Moreover, U.S. Pat. No. 4,770,764 discloses an additive obtained by mixing an aqueous heteropolyacid solution with a powdery carbonaceous substance in the anticipation that a high dispersion of the heteropolyacid in a hydrocarbon oil is attained by virtue of the activity of the carbonaceous substance powder as a carrier.
The heteropolyacid containing molybdenum atoms as polyatoms is a characteristic cluster compound having a single anion structure. In view of this structure, it can be anticipated that the heteropolyacid is suitable for use as a molybdenum catalyst precursor. However, despite such anticipation, the heteropolyacid is hydrophilic and oleophobic, so that it has high solubility in a hydrophilic solvent, such as water, an alcohol and an ether, but it is insoluble in a hydrocarbon oil. Therefore, it is difficult to attain a high dispersion of the heteropolyacid in a hydrocarbon feedstock only by adding to the hydrocarbon feedstock the heteropolyacid in the form of a solid or a solution thereof in a hydrophilic solvent. As a result, the hydroconversion activity of the heteropolyacid is unsatisfactory in the dispersion reaction system.
Despite the above various proposals hitherto made, any stable, continuous flow process which is completely satisfactory from the technical and practical viewpoints, has not yet been realized in the hydroconversion of a heavy hydrocarbon to a more valuable light hydrocarbon at a high conversion ratio, for example, a hydroconversion of a feedstock of vacuum distillation residual oil having a boiling point of 538.degree. C. (1000.degree. F.) or above to a hydrocarbon fraction having a boiling point of lower than 538 .degree. C. at a conversion ratio as high as 80%. The reason for the non-realization of such a continuous flow process is that when a hydroconversion at a high conversion ratio is attempted, the amount of polycondensates, such as coke and asphaltene, formed by side reactions is increased so that coking and choking phenomena attributed to adhesion and deposition of a portion of the polycondensates inside a reaction apparatus, particularly a reaction zone of the apparatus become extreme, and that effective measures have not been found for the suppression of such coking and choking phenomena.